Method of manufacturing electrode systems comprising semi-conductive bodies, more particularly crystal diodes or transistors

ABSTRACT

786,277. Semi-conductor devices. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Dec. 13, 1954 [Dec. 15, 1953; April 20, 1954], No. 35983/54. Class 37. A method of making a point contact semiconductor device, e.g. the diode shown, comprising a semi-conductor crystal 10, in which a part of the crystal is cleaned by removal of a surface layer as by grinding and/or etching and subsequently assembled in an envelope 17, is characterized in that the surface is covered immediately after cleaning with an insulating layer 16 and a point contact electrode 18 pushed through the layer to puncture it and in that the region around the puncture is subsequently occupied by a viscous insulating layer 21. In - the example shown, the crystal, originally in the form of a monocrystal Ge or Si sphere 10, is copper plated, soldered to connecting pin 12, ground to a flat surface, etched and immediately afterwards dipped in or sprayed with insulation 16, e.g. polystyrene in benzene. A layer 21 of viscous material, e.g. polymethyl siloxanes, is then applied to layer 16 and pin 12 and pin 19 bearing cat&#39;s-whisker 18 are inserted in metal sleeves 20 sealed in envelope 17 until the whisker punctures layer 16. The viscous layer is then consolidated by spinning the tube about axis Y. Instead of polystyrene or cellulose ester, alkyd resin or polyisobutylene may be used for the insulating layer.

METHOD OF MANUFACTURING ELECTRODE SYSTEMS COMPRISING SEMI-CONDUCTIVE BODIES, MORE PARTICULARLY CRYSTAL DIDES OR TRANSISTORS Filed D80. 29, 1954 Aug. 9, 1960 VAN VESSEM I'AL 2,948,050

' u INVENTORS JAN COENRAAD VAN VESSIEM THEQDORUS LE GRND AGENT United S ar-es Patt METHOD OF MANUFAC'I'URING ELECTRODE SYSTEMS COMPRISING SEMLCGNDUCTIVE BODIES, MORE PARTICULARLY CRYSTAL DIODES OR TRANSISTORS Jan Coenraad Van Vessem and Theodorus Le Grand,

Eindhoven, Netherlands, assignors, by mesne assignments, to North American Philips Company, Inc. New York, N.Y., a corporation of Delaware Filed Dec. 29, 1954, Ser. No. 478,424 Claims priority, applicatiou Netherlands Apr. 20, 1954 3 Claims. (Cl. 292s.3

Ths invention relates to methods of manufacturing electrode systemS comprising semiconductve bodies, more particularly crystal diodes or transistors, in which part of the surface of the semi-conductive body is cleaned, or example by grinding and/or etching. It is common practice to submit the semi-conductive bodies which may consist of, for example, germanium or silicon, to such a cleaning process before assembling the systems further, for example providing them with other electrodes and arranging them in an envelope.

However, the electrical properties of the completed systems may exhibit comparatively graat ditferences and this is naturally undesirable. The invention is based on recognition of the fact that the differences are largely attributable to atmospheric influences exerted upon the semi-conductive body during the time which elapses between cleaning and further assembling consisting in the rrangement of further electrodes and the incorporation ..1 an envelope.

The object of the invention is inter alia to avod the said disadvantage and to facilitate the manufacture of a uniform product.

According to the invention, the cleaned surface of the semi-conductive body is covered, immediately after cleaning, with a dense insulating layer which is removed, if necessary, in the further assembling of the systems. The influence exerted upon the said surface by the atmosphere is thus substantially elminated.

The dense layer may consist of a material which disappears during the further assembling of the systems, preferably as a result of an increase in temperature occurring during the assembling operation. The layer may, for exarnple, evaporate or combust.

If the electrode systems are of the kind in which at least one fused electrode is provided on the semiconductive body, the layer is preferably manufactured from a material which disappears below the melting temperature.

If the electrode system is of the kind in which one or more whiskers (point-contact electrodes) bear on the semi-conductive body, the whiskers are preferably pushed through the dense layer.

Sutable materials for manufacturing the layer are cellulose esters, polystyrene, alkyd resins, polyisobutylene and many other materials.

In this embodiment it may be advantageous for the dense insulating layer, which is not subject to deformation, to be covered with a viscous layer to prevent any contamination of the semi-conductive body, since contamination could still occur at the area, at which a whisker is pushed through the solid layer, more particularly since such whiskers are heated to a high tempera ture during the so-called forming process. The viscous layer may be caused to adhere rigidly to the solid insulating layer by centrifuging. It is preferably much thicker than the solid layer.

In order that the invention may be readily carried into effect, it will now be described with reference to the accompanying drawings showing, by w.ay of exarnple, two embodiments thereof.

Figs. 1 to 6 show diagrammatically the different stages of the manufacture of a transistor with electrodes melted thereon, a so-called alloy transistor.

Figs. 7 to 12 are analogous views of the manufacture of a diode having a whisker (point-contact electrode).

Fig. 13 is a cross-sectional view of another embodiment of a diode.

The initial product for the transistor is constituted by a small block of semieonductive material 1, for example germanium, which has been sawn from a monocrystal. The 'block is etched in the usual manner, so that a thin layer ndicated by dotted lnes in Fig. 1

disappears and a slightly smaller block remains (Fig. 2).

Immediately after etching, the block is covered with a dense layer 2, which consists, forexample, of nitrocellulose (Fig. 3). The block may thus be stored for a long period without being subject to the harmful influence of the atmosphere.

Afterwards, electrodes may be provided on the block by melting. 'Ihey may corisist, for example, of indium if the semiconductor is of germanium of the n-conduc- .and incorporated in an envelope in the usual manner.

The initial product for the diode is constituted by a grain of germanium 10, which is covered galvanically with a thin layer of copper 11 (Fig. 7). This grain is secured to the head of a carrier 12 with the use of a soldering agent 13, for example tin (Fig. 8). Subsequently, a plane surface 14 is ground on the side of the grain which is remote from the carrier (Fig. 9). The copper layer is not shown in this and following figures. Subsequently, the assembly is etched, as before, in the usual manner, resulting in a cleaned surface 15 (Fig. 10). The extremity of the carrier is then covered with a dense layer 16, for example by either dipping the carrier or sprayng it with a solution of polystyrene in benzene (Fig. 11). The resultant electrode with carrier is now protected against atmospheric influences.

Finally, the carrier 12, together with the semi-conductive body 10, is incorporated in an envelope 17 which is, for example, of glass. A second electrode in the form of a whisker 18, which is secured to a carrier 19, may without objection be pushed thr-ough the layer 16. The two carriers are in this case soldered in metallic tubes 20 sealed in the glass. In this case the use of the dense layer 16 affords the particular advantage that the semi-conductive body is also protected against the action of vapour which may be developed from the fusion agent used in soldering.

Fig. 13 shows a similar diode in which the dense and solid layer 16 is covered with a viscous layer or fill 21. The layer 21 may consist, for example, of so-called silicone grease, a mass c0nsistng of polymethyl siloxanes, which is commercially sold under the mark Dow Corning DC 4, 7 or 25. The layer 21, after having introduced the system into the envelope, is preferably caused to rigidly adhere by centrifuging about an axis Y-Y which is at right angles to the longitudinal axis XX of the diode.

It is observed that it is known to cover a carrier together with a semi-conductve body secured thereto with an insulating layer. However, such a layer was provided .before grin ding .or cl eaning the body, so that in this case the insulating layer did not exert a protecting influence upon the cleaned surface. It is also known for the whiskers of diodes or transistors, after being placed on the semi-conductive body, to be embedded in an insu1ting mass either for better securing thereof or for eliminating atmospheric influences. The harmful influence of the atmosphere during the time which elapses between the cleaning of the semi-conductive surface and the further assembling is in his case not eliminated either.

What is claimed is:

1. A method of manufacturing a semi-conductor device containing a point electrode in contact with a semiconductive body, which comprises subjecting at least a portion of the surface of said body to a treatment including etching wherein said surface portion is cleaned and polished and thereby becomes subject to contamination from various elements present in the atmosphere and the like, immediately thereafter covering said surface with a layerof dense, substantially atmospheric-proof, insulating material to thereby prevent said contaminating elements from contacting said cleaned surface portion, thereafter mounting said point electrode in contact with the seri1i-conductive body by urging said point electrode through the insulating layer into contact with said cleaned surface, thereafter surrounding the insulating layer with aviscous fi1l .to prevent said contaminating elements from contacting the cleaned surface through 1he aperture in the insulating layer formed by the point electrode, and

4 thereafter centrfuging the device to cause rigid adherence between the viscous fill and the insulating layer.

2. A method of making a semi-conductor device comprising a semi-conductive body, an electrode coupled to said body, and an envelope enclosng the body and electrode, comprising ntrodcing into said envelope a viscous, insultrig fillin a quantity sfiicieni to embrace the body and electrode and engage the surrounding envelope walls and fi11 the intervening space ciosing -the envelope, and thereafter centrifuging the device in 21 direction causing the viscous -fi11 rigidly to adhere to the body and envelope walls and thusprovide a dense fi1l affordng protection of the body.

3. A method as set forth in claim 2 wherein hedevice is elongated and has a longtudinal axis,.and the device is centrifuged about an axis extending at right angles to the said longitudnal axis.

References Cited in the file of this patent UNITED STATES PATENTS 1581,401 Mueller Apr. 20, 1926 1851509 Harnpton Mar. 29, 1932 2,31271O Gordon Mar. 2, 1943 2,406,405 Salisbury Aug. 27, 1946 2,419561 Jones et al. Apr. 29, 1947 2442,179 Shankl in May 25, 1948 2,741,686 North et al. Apr. 10, 1956 2,748326 Ingraham May 29, 1956 2,751,529 Stineman et al. June 19, 1956 2829,422 Fuller Apr. 8, 1958 2857,560 Schnable Oct. 21, 1958 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Jan Coenraao Van Vessem et al It is hereby certfied bhat error appears in the prinbed specifcacon of aha above numbered patent requiring correcton and that the sad Letters Patent should raad as corrected below.

for the indistinct word read Column l line 35 after "space" ;msert a comma column 4L line 9 1 ealed Lhis 11th day of April 1 (SEAL) Attest:

ARTHUR w. CROCKER Attesting Officer A ti Commissioner of Patents 

